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<div class="refentry">
<a name="boost.proto.fold.impl"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Struct template impl</span></h2>
<p>boost::proto::fold::impl</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../../proto/reference.html#header.boost.proto.transform.fold_hpp" title="Header &lt;boost/proto/transform/fold.hpp&gt;">boost/proto/transform/fold.hpp</a>&gt;

</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> State<span class="special">,</span> <span class="keyword">typename</span> Data<span class="special">&gt;</span> 
<span class="keyword">struct</span> <a class="link" href="impl.html" title="Struct template impl">impl</a> <span class="special">:</span> <span class="keyword"></span> <a class="link" href="../transform_impl.html" title="Struct template transform_impl">proto::transform_impl</a><span class="special">&lt;</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span> <span class="special">&gt;</span> <span class="special">{</span>
  <span class="comment">// types</span>
  <span class="keyword">typedef</span> <a class="link" href="../when.html" title="Struct template when">when</a><span class="special">&lt;</span><a class="link" href="../_.html" title="Struct _">_</a><span class="special">,</span> <span class="identifier">Sequence</span><span class="special">&gt;</span>                                        <a name="boost.proto.fold.impl.X"></a><span class="identifier">X</span><span class="special">;</span>            <span class="comment">// For exposition only</span>
  <span class="keyword">typedef</span> <a class="link" href="../when.html" title="Struct template when">when</a><span class="special">&lt;</span><a class="link" href="../_.html" title="Struct _">_</a><span class="special">,</span> <span class="identifier">State0</span><span class="special">&gt;</span>                                          <a name="boost.proto.fold.impl.Y"></a><span class="identifier">Y</span><span class="special">;</span>            <span class="comment">// For exposition only</span>
  <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span><span class="special">&lt;</span><span class="identifier">X</span><span class="special">(</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span><span class="special">)</span><span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span>    <a name="boost.proto.fold.impl.seq"></a><span class="identifier">seq</span><span class="special">;</span>          <span class="comment">// A Fusion sequence, for exposition only</span>
  <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span><span class="special">&lt;</span><span class="identifier">Y</span><span class="special">(</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span><span class="special">)</span><span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span>    <a name="boost.proto.fold.impl.state0"></a><span class="identifier">state0</span><span class="special">;</span>       <span class="comment">// An initial state for the fold, for exposition only</span>
  <span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span>                                              <a name="boost.proto.fold.impl.fun"></a><span class="identifier">fun</span><span class="special">;</span>          <span class="comment">// <code class="computeroutput">fun(d)(s,e) == when&lt;_,Fun&gt;()(e,s,d)</code></span>
  <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">fusion</span><span class="special">::</span><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">fold</span><span class="special">&lt;</span><span class="identifier">seq</span><span class="special">,</span> <span class="identifier">state0</span><span class="special">,</span> <span class="identifier">fun</span><span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span> <a name="boost.proto.fold.impl.result_type"></a><span class="identifier">result_type</span><span class="special">;</span>

  <span class="comment">// <a class="link" href="impl.html#id-1_3_34_5_45_2_1_1_5_9-bb">public member functions</a></span>
  <span class="identifier">result_type</span> <a class="link" href="impl.html#id-1_3_34_5_45_2_1_1_5_9_1-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">expr_param</span><span class="special">,</span> 
                         <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">state_param</span><span class="special">,</span> 
                         <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">data_param</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="id-1.3.34.5.47.4.4.3.4"></a><h2>Description</h2>
<div class="refsect2">
<a name="id-1.3.34.5.47.4.4.3.4.2"></a><h3>
<a name="id-1_3_34_5_45_2_1_1_5_9-bb"></a><code class="computeroutput">impl</code> public member functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="identifier">result_type</span> <a name="id-1_3_34_5_45_2_1_1_5_9_1-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">expr_param</span> expr<span class="special">,</span> 
                       <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">state_param</span> state<span class="special">,</span> 
                       <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">data_param</span> data<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<p>
                  Let <code class="computeroutput">seq</code> be
                  <code class="computeroutput"><code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">when</a></code>&lt;<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, Sequence&gt;()(expr, state, data)</code>,
                  let <code class="computeroutput">state0</code> be
                  <code class="computeroutput"><code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">when</a></code>&lt;<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, State0&gt;()(expr, state, data)</code>,
                  and let <code class="computeroutput">fun(data)</code> be an object such that
                  <code class="computeroutput">fun(data)(state, expr)</code> is equivalent to
                  <code class="computeroutput"><code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">when</a></code>&lt;<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, Fun&gt;()(expr, state, data)</code>. Then,
                  this function returns <code class="computeroutput">fusion::fold(seq, state0, fun(data))</code>.
                </p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><code class="computeroutput">data</code></span></p></td>
<td><p>An arbitrary data </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">expr</code></span></p></td>
<td><p>The current expression </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">state</code></span></p></td>
<td><p>The current state </p></td>
</tr>
</tbody>
</table></div></td>
</tr></tbody>
</table></div>
</li></ol></div>
</div>
</div>
</div>
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<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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